15,120 research outputs found
Stiffness of finite free resolutions and the Canonical Element Conjecture
Over a noetherian local ring certain minimal finite free resolutions possess
a property which we call stiffness. This calls to mind the Buchsbaum-Eisenbud
criterion for exactness. Yet we only prove stiffness over equicharacteristic
rings. However, Hochster's Canonical Element Conjecture is shown to be true for
every ring with a fixed prime residual characteristic, precisely when every
resolution over each Gorenstein ring of this type is stiff.Comment: 11 page
Using the Sun to estimate Earth-like planets detection capabilities. V. Parameterizing the impact of solar activity components on radial velocities
Stellar activity induced by active structures (eg, spots, faculae) is known
to strongly impact the radial velocity time series. It then limits the
detection of small planetary RV signals (eg, an Earth-mass planet in the
habitable zone of a solar-like star). In previous papers, we studied the
detectability of such planets around the Sun seen as an edge-on star. For that
purpose, we computed the RV and photometric variations induced by solar
magnetic activity, using all active structures observed over one entire cycle.
Our goal is to perform similar studies on stars with different physical and
geometrical properties. As a first step, we focus on Sun-like stars seen with
various inclinations, and on estimating detection capabilities with forthcoming
instruments. To do so, we first parameterize the solar active structures with
the most realistic pattern so as to obtain results consistent with the observed
ones. We simulate the growth, evolution and decay of solar spots, faculae and
network, using parameters and empiric laws derived from solar observations and
literature. We generate the corresponding structure lists over a full solar
cycle. We then build the resulting spectra and deduce the RV and photometric
variations for a `Sun' seen with various inclinations. The produced RV signal
takes into account the photometric contribution of structures as well as the
attenuation of the convective blueshift. The comparison between our simulated
activity pattern and the observed one validates our model. We show that the
inclination of the stellar rotation axis has a significant impact on the time
series. RV long-term amplitudes as well as short-term jitters are significantly
reduced when going from edge-on to pole-on configurations. Assuming spin-orbit
alignment, the optimal configuration for planet detection is an inclined star
(i~45{\deg}).Comment: Accepted to Astronomy and Astrophysics on May, 27th 2015. The
manuscript includes 22 pages, 20 figure
Stellar populations in the center of barred spiral galaxies
We show observations obtained with the integral field spectrometer OASIS for
the central regions of a sample of barred galaxies. The high spatial resolution
of the instrument allows to distinguish various structures within these regions
as defined by stellar populations of different ages and metallicities. From
these data we obtain important clues about the star formation history. But we
advise that, in order to obtain adequately the evolutionary sequence, a
combination of chemical and synthesis models may be necessary.Comment: 4 pages, 2 figures, submitted to the IAU245 Symposium Formation and
Evolution of Galaxy Bulge
Laser Doppler Velocimetry for Joint Measurements of Acoustic and Mean Flow Velocities : LMS-based Algorithm and CRB Calculation
This paper presents a least mean square (LMS) algorithm for the joint
estimation of acoustic and mean flow velocities from laser doppler velocimetry
(LDV) measurements. The usual algorithms used for measuring with LDV purely
acoustic velocity or mean flow velocity may not be used when the acoustic field
is disturbed by a mean flow component. The LMS-based algorithm allows accurate
estimations of both acoustic and mean flow velocities. The Cram\'er-Rao bound
(CRB) of the associated problem is determined. The variance of the estimators
of both acoustic and mean flow velocities is also given. Simulation results of
this algorithm are compared with the CRB and the comparison leads to validate
this estimator
Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample
Massive, Main-Sequence AF-type stars have so far remained unexplored in past
radial velocity surveys, due to their small number of spectral lines and their
high rotational velocities that prevent the classic RV computation method. Our
aim was to search for giant planets around AF MS stars, to get first
statistical information on their occurrence rate and to compare the results
with evolved stars and lower-mass MS stars. We used the HARPS spectrograph
located on the 3.6m telescope at ESO La Silla Observatory to observe 108 AF MS
stars with B-V in the -0.04 to 0.58 range and masses in the range 1.1-3.6 Msun.
We used our SAFIR software specifically developed to compute the radial
velocities of these early-type stars. We report the new detection of a mpsini =
4.51 Mjup companion with a ~826-day period to the F6V dwarf HD111998. We
present new data on the 2-planet system around the F6IV-V dwarf HD60532. We
also report the detection of 14 binaries with long-term RV trends. 70% of our
targets show detection limits between 0.1 and 10 Mjup in the 1 to 10^3-day
range. We derive brown dwarf (13 < mpsini < 80 Mjup) occurrence rates in the 1
to 10^3-day range of % and % for stars with
masses in the ranges 1.1-1.5 and 1.5-3 Msun, respectively. As for Jupiter-mass
companions (1 < mpsini < 13 Mjup), we get occurrence rates in the 1 to 10^3-day
range of % and % respectively for the same
stellar mass ranges. When considering the same Jupiter-mass companions but
periods in the 1 to 100-day range only, we get occurrence rates of
% and %. Given the present error bars, these
results do not show a significant difference with companion frequencies derived
for solar-like stars.Comment: 23 pages (text), 15 figures, accepted in Astronomy and Astrophysic
Resourceful leadership: how directors of children’s services improve outcomes for children, full report
Leading for Outcomes is a unique study into senior leadership in children’s services in England, drawing on in-depth primary research with leaders in eight local authorities, and 22 directors of children’s services. The eight local authorities were selected on a range of factors but primarily to represent existing high performers or rapidly improving authorities in terms of outcomes. The research was commissioned by the National College in partnership with C4EO, and completed by a team comprising Deloitte, Navigate and the University of Oxford. The study was completed during 2010.
The key concept the Leading for Outcomes research has uncovered is that of the resourceful leader1. This report sets out a definition of resourcefulness and the eight core behaviours of resourceful leaders. It then discusses resourcefulness within three specific contexts that emerged as part of the research: leading change, leading in a time of shock, and managing the corporate and political landscape
Measuring physical inactivity:do current measures provide an accurate view of "sedentary" video game time?
BACKGROUND: Measures of screen time are often used to assess sedentary behaviour. Participation in activity-based video games (exergames) can contribute to estimates of screen time, as current practices of measuring it do not consider the growing evidence that playing exergames can provide light to moderate levels of physical activity. This study aimed to determine what proportion of time spent playing video games was actually spent playing exergames. METHODS: Data were collected via a cross-sectional telephone survey in South Australia. Participants aged 18 years and above (n = 2026) were asked about their video game habits, as well as demographic and socioeconomic factors. In cases where children were in the household, the video game habits of a randomly selected child were also questioned. RESULTS: Overall, 31.3% of adults and 79.9% of children spend at least some time playing video games. Of these, 24.1% of adults and 42.1% of children play exergames, with these types of games accounting for a third of all time that adults spend playing video games and nearly 20% of children's video game time. CONCLUSIONS: A substantial proportion of time that would usually be classified as "sedentary" may actually be spent participating in light to moderate physical activity
Towards redistribution laser cooling of molecular gases: Production of candidate molecules SrH by laser ablation
Laser cooling by collisional redistribution of radiation has been
successfully applied in the past for cooling dense atomic gases. Here we report
on progress of work aiming at the demonstration of redistribution laser cooling
in a molecular gas. The candidate molecule strontium monohydride is produced by
laser ablation of strontium dihydride in a pressurized noble gas atmosphere.
The composition of the ablation plasma plume is analyzed by measuring its
emission spectrum. The dynamics of SrH molecular density following the ablation
laser pulse is studied as a function of the buffer gas pressure and the laser
intensity.Comment: Laser Refrigeration of Solids VI, February 2 2013, San Francisco,
USA, Conference Proceeding
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